The combustion chamber is a lean pre-mix, two-stage design concept with a lean fuel/air mixture in both stages, so that the lowest possible level of pollution is achieved, for all engine conditions from idle to full load.
In order to minimize pollution (NOx) it is important to ensure a fully vaporized and uniform mixture of air and fuel. This is achieved by the use of a venturi nozzle, which ensures a velocity difference between the fuel drops and the air, due to the inertia of the fuel.
Previously, a swirler was used to introduce the secondary fuel/air mixture into the primary flame. This gave the mixture an angular momentum at exit to the venturi, which counteracted the rotation from the primary flame and forced the heavier unburnt mixture outwards due to the effect of centrifugal force. The swirler was costly to produce, had mechanical problems with attachment, showed a tendency to produce unacceptable pulsations, and was vulnerable to burn-out.
EP application 445 652 describes a device for combustion chambers of gas turbines with transverse mixing tubes to a central mixing tube, where the mixing tubes resemble venturi nozzles and where the secondary venturi has a swirler.